# The Cosmic Perspective, 7e (Bennett et al.) Supplement 4: Building Blocks of the Universe

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 The Cosmic Perspective, 7e (Bennett et al.) Supplement 4: Building Blocks of the Universe S4.1 Multiple-Choice Questions 1) Quantum mechanics is A) a branch of physics that applies on very small scales. B) the idea that mechanics can be understood only if we first understand quantums. C) the idea that quantitative methods are needed to understand physics. D) a branch of physics that deals with the curvature of spacetime. E) a branch of physics that deals with the properties of gases. Answer: A 2) The primary purpose of a particle accelerator is to A) make small particles go very fast. B) make small particles achieve large accelerations. C) create particles and study their behavior. D) produce energy for commercial use. E) test new ideas about the law of gravity. Answer: C 3) Which of the following statements best describes the quantum property spin? A) Spin is a measure of the rotation rate of a subatomic particle. B) Spin is a measure of the rate at which a particle spins around (orbits) another particle. C) Spin is a property that applies only to large objects, like baseballs. D) Spin is not meant to be taken literally but measures the inherent angular momentum of a subatomic particle. E) Spin is not a fundamental property but rather something that can change randomly at any time. Answer: D 4) The characteristic that distinguishes fermions from bosons is A) their mass. B) their electric charge. C) their spin. D) their size. E) their speed of travel. Answer: C 5) An up quark (u) has a charge +2/3, and a down quark (d) has a charge of —1/3. Which of the following describes a proton? A) uuu B) uud C) udd D) ddd Answer: B 6) An up quark (u) has a charge of +2/3 and a down quark (d) has a charge of —1/3. Which of the following describes a neutron? A) uuu B) uud C) udd D) ddd Answer: C 7) Protons and neutrons A) have exactly the same mass. B) have exactly the same charge. C) are composed of the same number of quarks. D) are fundamental particles. E) are leptons. Answer: C 8) Which of the following statements about electrons is not true? A) Electrons carry a negative charge. B) In an atom, an electron can have two possible values for its spin, usually called spin up and spin down. C) Electrons are one of the six known types of lepton. D) Electrons have about the same mass as protons. E) Electrons are both particles and waves. Answer: D 9) Which of the following statements about neutrinos is not true? A) Neutrinos are neither attracted nor repelled by electrically charged particles. B) Neutrinos have a mass that is much smaller than the mass of an electron. C) Neutrinos do not respond to the strong nuclear force. D) There are three types of neutrinos, and these represent three of the six known types of lepton. E) Neutrinos do not respond to the force of gravity. Answer: E 10) The mass of a neutrino is A) equal to the mass of an electron. B) equal to the mass of a proton. C) equal to the mass of a neutron. D) less than the mass of an electron but its actual value is unknown. E) zero. Answer: D 11) The two families of fundamental particles out of which all ordinary matter is made are A) protons and neutrons. B) leptons and quarks. C) electrons and neutrinos. D) quarks and neutrinos. E) leptons and photons. Answer: B 12) What happens when a particle and its corresponding particle of antimatter meet? A) No one knows, since antimatter is only theoretical and not known to really exist. B) The particles join together to make an antimatter atom. C) The particles collide and then bounce back apart. D) The particle and the antiparticle are annihilated, turning all their mass into energy. E) They live happily ever after. Answer: D 13) The four fundamental forces are A) strong force, weak force, electric force, magnetic force. B) strong force, weak force, electromagnetic force, gravity. C) nuclear force, electromagnetic force, gravity, tidal force. D) nuclear force, gravity, tidal force, magnetic force. Answer: B 14) Which of the following is not a fundamental force? A) strong force B) weak force C) degeneracy pressure D) electromagnetic force E) gravity Answer: C 15) Which force is strongest within an atomic nucleus? A) strong B) weak C) electromagnetic D) gravity E) They are all equal. Answer: A 16) Which force is strongest beyond an atomic nucleus? A) strong B) weak C) electromagnetic D) gravity E) They are all equal. Answer: C 17) Which of the following is not an exchange particle (that mediates the four fundamental forces of nature)? A) gravitons B) photons C) leptons D) weak bosons E) gluons Answer: C 18) Suppose that, through the malicious act of an eight-dimensional alien being, the strong force was suddenly turned off throughout the universe. What would happen almost immediately to atoms? A) nothing B) Electrons would fall into the nuclei of atoms. C) Atoms would be immediately ionized. D) The nuclei of atoms would fall apart. E) Gravity would become the strongest force in nature. Answer: D 19) The two fundamental laws that lie at the heart of quantum mechanics are A) the absoluteness of the speed of light and the equivalence principle. B) the law of conservation of energy and the electromagnetic force law. C) the uncertainty principle and the exclusion principle. D) the law of conservation of angular momentum and the law of conservation of energy. E) the law of quantum degeneracy and the law of inviolate absolutes. Answer: C 20) According to the uncertainty principle, which of the following statements is true? A) God does not play dice. B) It is impossible to measure both the position and the velocity of a particle at the same time. C) It is impossible to measure both the mass and the velocity of a particle at the same time. D) It is impossible to measure both the speed and the direction of a particle at the same time. E) It is impossible for science to make any meaningful predictions about nature whatsoever. Answer: B 21) Which of the following best describes the meaning of the uncertainty principle as applied to an electron bound in an atom? A) The electron follows a precise path around the nucleus, but it is impossible for us to actually measure this path. B) The electron is actually a precisely defined sphere surrounding the nucleus rather than a point, which explains why we cannot locate it at a single position. C) The electron always has a clearly defined position and velocity, but the laws of nature are set up so that, if we measure one, the other becomes instantly hidden from view. D) The electron does not really exist, and what we perceive as an electron is really just an ill-defined energy field. E) The electron is both a particle and a wave and is therefore "smeared out" around the nucleus. Answer: E 22) Why doesn't the uncertainty principle affect our ability to follow the path of a baseball? A) The uncertainty principle applies only to subatomic particles. B) The uncertainties in all the individual atoms within the baseball cancel each other out. C) The uncertainties in the position and momentum of the baseball are so small in comparison to its size and total momentum that they are unnoticeable. D) The exclusion principle says that large objects are excluded from the consequences of the uncertainty principle. E) The uncertainty principle does not have anything to do with following the path of a particle or an object. Answer: C 23) What law of nature explains why electrons must arrange themselves in atoms with no more than two per energy level, thus making chemistry possible? A) the exclusion principle B) the uncertainty principle C) the law of conservation of energy D) the law of conservation of angular momentum E) the electromagnetic force law Answer: A 24) Which of the following statements best describes the exclusion principle? A) If a particle has a precisely defined position, it is excluded from having a precisely defined momentum. B) The laws of quantum mechanics are excluded from applying to large objects made of many atoms. C) Two fermions cannot occupy the same quantum state at the same time. D) Two photons cannot be in the same place at the same time. E) The laws of quantum mechanics are excluded from our common sense. Answer: C 25) Which of the following will cause the degeneracy pressure within an object to increase? A) raising its temperature B) lowering its temperature C) compressing it to higher density D) letting it expand to lower density E) shining a light on it, which adds radiative energy Answer: C 26) Why is there a limit to how much compression can be counterbalanced by electron degeneracy pressure? A) At extreme compression, the electron speeds approach the speed of light and therefore cannot increase further. B) At extreme compression, electrons are forced to stop moving, and once stopped there is nothing more they can do. C) At extreme compression, atoms are fully ionized, so electrons go free and can no longer exert pressure. D) The exclusion principle excludes electrons from exerting more pressure than the uncertainty principle would otherwise allow. E) Electrons are very small and are simply incapable of exerting much pressure. Answer: A 27) Which of the following statements about degeneracy pressure is not true? A) Explaining the origin of degeneracy pressure requires both the quantum mechanical exclusion principle and the uncertainty principle. B) Degeneracy pressure stops the gravitational collapse of white dwarfs. C) Degeneracy pressure stops the gravitational collapse of ordinary (main-sequence) stars like the Sun. D) Degeneracy pressure halts the collapse of neutron stars. E) Degeneracy pressure arises only with fermions (such as electrons, protons, and neutrons) and not with bosons (such as photons or helium nuclei). Answer: C 28) Which of the following statements about quantum tunneling is true? A) It is used in modern electronics, and, in fact, our modern-day computers would not work without it. B) It plays a crucial role in nuclear fusion in the Sun. C) It allows electrons and other subatomic particles to pass through wall-like energy barriers even when it seems they do not have enough energy to get through the barriers. D) Although it has been observed to occur, it violates all other known laws of nature, and explaining it therefore represents a major challenge to physicists. E) A, B, and C are true, but D is not Answer: E 29) Which of the following best explains the phenomenon of black hole evaporation? A) Due to high temperatures in the accretion disk around a black hole, material evaporates from the black hole like water evaporating from the ocean. B) Particles (or antiparticles) are occasionally ejected from within the event horizon, causing the black hole to lose mass. C) Particles (or antiparticles) are created by a quantum mechanical effect near, but outside, the event horizon of the black hole. The law of conservation of energy maintains that the black hole must lose energy to "pay" for the creation of this mass. D) Virtual particles created near the black hole are constantly annihilating each other, causing a very high temperature even if the black hole has no accretion disk. This high temperature provides escape velocity for the virtual particles, causing the entire "cloud" of virtual particles to expand away into space. E) Black hole evaporation is a virtual process, meaning that it has been theorized by astrophysicists but doesn't really occur. Answer: C 30) Which of the following statements about Hawking radiation is not true, at least according to our current understanding? A) It was first predicted by Stephen Hawking in the 1970s. B) It causes black holes to slowly shrink in mass. C) It has never yet been observed. D) It represents a strange form of radiation that emerges from within the event horizon of a black hole. E) It occurs when real particles are created from the gravitational potential energy of a black hole. Answer: D S4.2 True/False Questions 1) The electromagnetic force is the force that holds nuclei together. Answer: FALSE 2) The number of neutrinos in the universe is greater than all the protons, neutrons, and electrons combined. Answer: TRUE 3) The basic building blocks of matter are protons, neutrons, and electrons. Answer: TRUE 4) To our current knowledge, antimatter does not really exist; it is purely science fiction. Answer: FALSE 5) Fermions obey the exclusion principle, but bosons do not. Answer: TRUE 6) The thermal pressure in an object increases when the temperature increases, but the degeneracy pressure does not. Answer: TRUE 7) Since it was first predicted in the 1970s, scientists have observed the evaporation of about a dozen black holes. Answer: FALSE 8) Although we cannot see virtual particles, some experimental evidence suggests that they really exist. Answer: TRUE S4.3 Short Answer Questions 1) The strong nuclear force is the force that holds the protons and neutrons in the nucleus together. Based on the fact that atomic nuclei can be stable, briefly explain how you can conclude that the strong force must be even stronger than the electromagnetic force, at least over very short distances. Answer: An atomic nucleus is made of protons and neutrons. The neutrons have no charge, but protons are positively charged. Thus, if it were just up to the electromagnetic force, a nucleus would fall apart due to the repulsion between the positive protons. Since the strong force is holding the nucleus together despite the electromagnetic repulsion, it must be the stronger (per particle) force within the nucleus. Note that this strength holds only over distances roughly the size of an atomic nucleus. Over larger distances, the strong force cannot be felt at all. 2) All chemical and biological reactions involve the creation and breaking of chemical bonds, which are bonds between the electrons of one atom and the electrons of others. Given this fact, explain why the electromagnetic force governs all chemical and biological reactions. Also explain why the strong force, the weak force, and gravity play no role in these reactions. Answer: Gravity is far too weak to play a role in creating and breaking bonds between atoms or molecules; in fact, its only role in life is in keeping us "stuck" to the ground. The nuclear forces are of such short range that they have no effects outside the nucleus itself. The only force that remains is the electromagnetic force, which influences interactions between the charged electrons and nuclei. Thus, all events in our ordinary lives–all chemistry and biology–are dominated by the electromagnetic force. 3) The electromagnetic force between two charged particles is much greater than the strength of gravity between them, no matter how far apart they are. Nevertheless, it is gravity, rather than the electromagnetic force, that dominates the universe on large scales. Briefly explain why. Answer: Despite its far greater strength per particle, the electromagnetic force is unable to attain very large values because it is impossible to accumulate a very large charge. This is because large objects tend to have equal amounts of positive (protons) and negative (electrons) charge, and the electromagnetic force thus "cancels" itself out. Gravity, on the other hand, always attracts: As objects get more and more massive, gravity continues to gain strength. Thus, for very large objects, there will be a great deal of gravitational attraction but virtually no electromagnetic force, since the overall object is neutral. 4) Briefly state the uncertainty principle. Answer: The more we know about where a particle is located, the less we can know about its momentum, and the more we know about its momentum, the less we can know about its position. 5) What is quantum tunnelling? Answer: Quantum tunnelling is the name given to the mechanism by which small particles can overcome energy barriers. For example, an electron in a low energy level can occasionally "tunnel" through an energy barrier to a higher energy level. The effect arises because the absolute energy of an object is never precisely known because of the uncertainty principle. The uncertainty, in absolute terms, is very small, but for quantum particles, the relative uncertainty can be significant and occasionally allows a particle to "jump over" an energy barrier. 6) What is "Hawking radiation"? Answer: The uncertainty principle allows for virtual particles to pop in and out of existence on extremely short timescales anywhere in space. The production of such particles near the event horizon of a black hole can result in one of the pair entering the black hole and the other remaining outside. Without its virtual partner, this particle becomes a "real" part of space (its mass is equivalent to the gravitational energy lost by its other half falling to the center of the black hole). By symmetry we expect equal numbers of matter and anti-matter particles to form around the black hole and these will eventually meet and annihilate each other, producing what is termed Hawking radiation. The creation of mass-energy from a quantum fluctuation comes at the expense of the black hole which (very slowly) evaporates. 7) Briefly explain how antimatter can be produced by scientists. Answer: Antimatter is produced in particle accelerators. When particles collide and release large amounts of energy in one place, some of the energy spontaneously turns into mass. This mass must contain particles and their antiparticles in equal quantities. 8) Briefly explain why antimatter is difficult to store after it is produced in laboratories. Answer: When matter and antimatter meet, the result is mutual annihilation. Because everything on Earth is made of ordinary matter, it is difficult to prevent antimatter produced in the lab from contacting matter and quickly becoming annihilated. 9) Process of Science: The idea of quantum tunneling seems very counterintuitive. However, there is considerable evidence to support it. Describe one such line of evidence. Answer: Answers will vary, but may include discussion of fusion in the Sun, or uses in modern technology such as microchips. 10) Process of Science: Why do scientists believe that black holes can't last forever, and do they have any observational evidence to support this idea? Answer: Scientists surmise that if a particle-antiparticle pair came into existence near an event horizon and one particle crossed the horizon before they could annihilate, the source of energy for the surviving particle would be the black hole itself. This is called Hawking radiation. The theoretical grounding of this idea is strong, but it has not yet been observed. 11) Process of Science: Why is String Theory not really a theory? Answer: Most of the predictions of string theory cannot be observed using current particle accelerators such as the Large Hadron Collider. Therefore it is more a hypothesis than a bona fide theory. 12) Process of Science: The "standard model” that describes the building blocks of nature works extremely well and has been most recently verified through the discovery of the Higgs boson. Why, then, do some scientists continue to search for a simpler model? Answer: This is basically Occam's razor: the standard model has many fundamental particles and some scientists believe that the ultimate description of nature should be simpler with a unified force that explains all particle interactions. S4.4 Mastering Astronomy Reading Quiz 1) What is the primary topic of study in quantum mechanics? A) the role played by atoms in astronomy B) subatomic particles and the forces with which they interact C) the mechanical movements of the heavens D) the role of relativity in astronomy Answer: B 2) What do we mean by the spin of a subatomic particle? A) It describes how fast the particle is rotating on its axis at a given time—if more torque is applied, the particle spins faster. B) It is one of the basic properties of any particle, and is a measure of the particle's angular momentum. C) It is a measure of the particle's electrical charge. D) The spin of a particle describes how the story of the particle is portrayed to journalists. Answer: B 3) Based on their spin, all particles fall into which of the following categories? A) quarks and leptons B) fermions and bosons C) matter and antimatter D) color, flavor, and mass Answer: B 4) According to modern understanding, protons and neutrons are each composed of A) three leptons. B) two fermions. C) three quarks. D) four bosons. Answer: C 5) Which of the following is not considered a fundamental particle? A) an electron B) an up quark C) a neutrino D) a proton Answer: D 6) Which statement about antimatter is not true? A) An antielectron (positron) is identical to an ordinary electron except it has a positive charge. B) Every ordinary particle has a corresponding antiparticle. C) When a particle and its antiparticle meet, the result is mutual annihilation that turns all of the mass into energy. D) Antimatter has been hypothesized to exist but has never actually been detected. Answer: D 7) The four fundamental forces are A) strong force, weak force, electromagnetic force, gravity. B) strong force, weak force, electric force, magnetic force. C) nuclear force, electromagnetic force, gravity, tidal force. D) nuclear force, gravity, electric force, magnetic force. Answer: A 8) What are the two fundamental laws that lie at the heart of quantum mechanics? A) the uncertainty principle and the exclusion principle B) the absoluteness of the speed of light and the equivalence principle C) the law of conservation of energy and the electromagnetic force law D) the law of conservation of angular momentum and the law of conservation of energy Answer: A 9) According to the uncertainty principle, which of the following statements is true? A) It is impossible to measure both the mass and the momentum of a particle at the same time. B) It is impossible to measure both the position and the momentum of a particle at the same time. C) It is impossible for science to make any meaningful predictions about nature whatsoever. D) It is impossible to measure both the speed and direction of a particle at the same time. Answer: B 10) An alternative statement of the uncertainly principle tells us that we cannot know precisely both A) a particle's mass and energy. B) whether a particle is a wave or whether it is truly a particle. C) a particle's energy and the time during which it has this energy. D) a particle's momentum and its energy. Answer: C 11) What does the exclusion principle say? A) No two particles of any type can ever occupy the same quantum state at the same time. B) If a particle has a precisely defined position it is excluded from having a precisely defined momentum. C) The laws of quantum mechanics are excluded from our common sense. D) Two fermions cannot occupy the same quantum state at the same time. Answer: D 12) How does degeneracy pressure differ from thermal pressure? A) Degeneracy pressure cannot support an object against the crush of gravity, but thermal pressure can. B) Degeneracy pressure can arise in a plasma, but thermal pressure cannot. C) Degeneracy pressure affects stars, but thermal pressure does not. D) Degeneracy pressure continues to be felt even if an object becomes very cold, but thermal pressure is drastically reduced as an object gets cold. Answer: D 13) How is quantum tunneling important to our existence here on Earth? A) It explains how neutron stars are able to stay stable rather than collapsing under their strong gravity. B) It explains why electrons in atoms gradually fill different energy levels, thus making chemistry possible. C) It plays a crucial role in nuclear fusion in the Sun, so that our Sun would not shine brightly without it. D) It is very important to understanding the law of conservation of energy. Answer: C 14) What is Hawking radiation? A) a type of high-energy radiation that comes from inside a black hole's event horizon B) a type of radiation coming from objects supported by degeneracy pressure C) a hypothesized way for black holes to gradually shrink in mass D) a type of radiation that we have detected so far only with infrared telescopes in space Answer: C S4.5 Mastering Astronomy Concept Quiz 1) Given that many of the ideas of quantum mechanics seem so strange to our intuition, why do scientists think these ideas are correct? A) Quantum ideas can be used to make precise predictions that have been tested and confirmed through observations and experiments. B) Although the ideas seem strange at first, they make perfect sense once they are studied in depth, which is why scientists accept them. C) Quantum ideas were expected to be strange, so the fact that they are strange only lends them support. D) Actually, very few scientists think the quantum ideas are correct, and most expect the theories of quantum mechanics to be completely replaced in the near future. Answer: A 2) Which of the following is not one of the basic properties by which we classify a subatomic particle? A) mass B) charge (electrical) C) spin D) temperature Answer: D 3) The primary scientific purpose of a particle accelerator is to A) make small particles achieve large accelerations. B) produce energy for commercial use. C) create particles and study their behavior. D) make small particles go very fast Answer: C 4) Which of the following statements about electrons is not true? A) In an atom, an electron can have two possible values for its spin, usually called spin up and spin down. B) Electrons are one of the 6 known types of lepton. C) They are composed of quarks. D) Electrons can behave both as particles and as waves. Answer: C 5) Recall that an up quark (u) has a charge of +2/3 and a down quark (d) has a charge of -1/3. Which of the following quark compositions describes a proton? A) uuu B) uud C) udd D) uuudd Answer: B 6) Suppose that, through the malicious act of an eight-dimensional alien being, the strong force was suddenly turned off throughout the universe. What would happen almost immediately to atoms? A) Electrons would fall into the nuclei of atoms. B) The nuclei of atoms would fall apart. C) Atoms would be immediately ionized. D) Nothing; atoms would be unaffected by this change. Answer: B 7) The force of gravity is the only one of the four forces felt on very large size scales. Which of the following best explains why the other forces don't play a major role on large scales? A) The other three forces are all very short in range, and cannot be felt over large distances. B) The strong and weak forces act only on very small scales, and large objects tend to be electrically neutral and therefore don't feel an electromagnetic force. C) Gravity is by far the strongest force, so it simply dominates on large size scales. D) Effects of the strong and weak forces tend to cancel out effects of the electromagnetic force on large scales. Answer: B 8) Does the uncertainty principle affect our ability to follow the path of a baseball? Why or why not? A) No, because the uncertainties in the position and momentum of the baseball are so small in comparison to its size and total momentum that they are unnoticeable. B) Yes, because we cannot know both where the baseball is and which way it is going at the same time. C) No, because the exclusion principle says that large objects are excluded from the consequences of the uncertainty principle. D) No, because the uncertainty principle applies only to electrons. Answer: A 9) All the following statements are true. Which one can be attributed to the exclusion principle? A) If we know the location of an electron quite well, we will have little idea where it is going next. B) If an electron and antielectron meet, they will turn into energy through mutual annihilation. C) An electron has energy equal to its mass times the speed of light squared. D) Two electrons with the same spin cannot occupy the same energy level in an atom. Answer: D 10) What else always happens when an electron is produced from energy in a particle accelerator? A) The electron quickly becomes part of an atom. B) The electron releases a tremendous amount of energy. C) An antielectron (positron) is also produced. D) The electron begins moving at extremely high speed. Answer: C 11) Uh-oh, the malicious eight-dimensional alien beings are back. This time, imagine that they suddenly changed nature so that neither the uncertainty principle nor the exclusion principle applied to electrons. What would happen almost immediately to atoms? A) Atoms would annihilate each other, releasing huge amounts of energy. B) Atoms would be immediately ionized. C) Nothing; atoms would be unaffected by this change. D) Electrons would fall into the nuclei of atoms. Answer: D 12) Why is there a limit to how much compression can be counterbalanced by electron degeneracy pressure? A) At extreme compression, the electron speeds approach the speed of light and therefore cannot increase further. B) At extreme compression, electrons are forced to stop moving, and once stopped there is nothing more they can do. C) At extreme compression, atoms are fully ionized so that electrons go free and can no longer exert pressure. D) Because electrons are very small, they are simply incapable of exerting much pressure. Answer: A 13) Which of the following statements about quantum tunneling is not true? A) It is used in modern electronics and, in fact, our modern-day computers would not work without it. B) Although it has been observed to occur, it violates all other known laws of nature and explaining it therefore represents a major challenge to physicists. C) It plays a crucial role in nuclear fusion in the Sun. D) It allows electrons and other subatomic particles to pass through wall-like energy barriers even when it seems they do not have enough energy to get through the barriers. Answer: B 14) Which of the following best explains the hypothesized phenomenon of black hole evaporation? A) Particles (or anti-particles) are occasionally ejected from within the event horizon, causing the black hole to lose mass. B) Virtual particles created near the black hole are constantly annihilating each other, causing a very high temperature even if the black hole has no accretion disk. This high temperature provides escape velocity for the virtual particles, causing the entire "cloud" of virtual particles to expand away into space. C) Particles (or anti-particles) are created by a quantum mechanical effect near, but outside, the event horizon of the black hole. The law of conservation of energy maintains that the black hole must lose energy to "pay" for the creation of this mass. D) Black hole evaporation is a virtual process, meaning that it has been theorized by astrophysicists, but doesn't really occur. Answer: C Copyright © 2014 Pearson Education, Inc.

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